1. Field of the Invention
The present invention relates to speed variators which permit an infinite number of speed ratios between two different rotary shafts over a more or less broad range. Speed variators of this type have a very large number of potential applications. They may thus be employed in motor vehicles or in cycles, or else in any machines or mechanical devices.
2. Description of the Prior Art
More precisely, the invention is concerned with speed variators of the type comprising two elements consisting respectively of a driving element and a driven element rotatably mounted on two parallel axes, one of which is displaceable with respect to the other. These two elements are connected to each other by means of a series of driving crank-arms pivotally coupled at one end with one of said elements at different points of a circle having the same axis whilst their opposite end is intended to be coupled with the other element at a point of a circle having the same axis as said element, by virtue of unidirectional coupling means. Thus the variation in spacing between the axes of the two elements (driving and driven element) of this variator permits a continuous variation of the transmission ratio of this latter.
European patent EP 208,473 describes a speed variator of this type. In this device, one of the rotating transmission elements carries a series of articulated arms, the ends of which constitute pawls which are intended to engage with a ratchet wheel provided with an internal set of teeth. Modification of the eccentric position of one of the rotating elements with respect to the other produces a variation of the angular position of the coupling arms and consequently a variation of the transmission ratio.
However, this solution is subject to a certain number of disadvantages. One of these lies in the fact that coupling between the two rotary transmission elements takes place only when the pawl in service is engaged at the bottom of a space between two teeth of the ratchet wheel. Moreover, this solution does not offer fully satisfactory mechanical strength since the teeth of the ratchet wheel are subjected to extremely high stresses.
It is for these reasons that the present invention is concerned with a variator which is so designed as to remove these drawbacks.